Filling Old Transducer Hole

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John, CD28
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Filling Old Transducer Hole

Post by John, CD28 »

I've got to fill an old 2" transducer hole below the waterline. I'm ok with grinding out a large bevel, wetting it out with epoxy, then laying/wetting in consecutively larger circles of biaxial, and finishing off with some epoxy fairing compound.

A YouTube video from Jamestown Distributors/West Systems has me confused. The video shows them building/wetting up the new layers of glass on a table, then placing the assembled patch into the beveled hole big circle first. I'm not going to question Jamestown, or West System, but I was thinking the smallest circles of biaxial would go in the hole first with larger circles on top, up to the outer surface of the hull.

Does it make a difference if the small patches go in first or last? Any thoughts or ideas before I jump into this project?

Link to YouTube video: http://youtu.be/6N7YMr6E564

Much appreciated,
John
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Re: Filling Old Transducer Hole

Post by okawbow »

I start with the large patch first, and then smaller and smaller. That way, you get full contact on the hull with the first patch. The rest of the patches will stick better to the other patches than they would to the edge of the hole. I sometimes let the finished patch come out slightly below level, and then add 1 large patch over the whole thing to tie it together better.

I filled 10 through hulls in my Privateer 26 schooner hull that way. They seem as solid as the rest of the hull.
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Re: Filling Old Transducer Hole

Post by earlylight »

John,
The video and Chuck are correct for the reason that Chuck mentions. (The first large patch gets a much larger bonding area to the hull). I filled two holes from unused sea-cocks and one from a knot-meter paddle wheel transducer on my previous boat and the repairs were as solid as the hull itself after 11 years.
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Re: Filling Old Transducer Hole

Post by CharlieJ »

And one more for the large piece first. Seven holes in Tehani's bottom, and 3 in my trailerable sloop were all done that way.

If you put the small patch in first, when you smooth down, you grind away the contact parts of the rest of the patches. Stronger done largest first.
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Re: Filling Old Transducer Hole

Post by John, CD28 »

That does make sense - all the surface area of the large patch grabbing the hull, rather than all the little edges of all the patches.

Large patch first it is then.

Thanks again!
John
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Re: Filling Old Transducer Hole

Post by John, CD28 »

One other question:

If I layer up the patch, then place it into the ground/beveled hole as in the Jamestown video, how do I know how many layers to use? How do I get the thickness right before putting it into the beveled hole?

Any ideas?

John
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Re: Filling Old Transducer Hole

Post by Carl-A259 »

John , If you're asking all these questions, I wouldn't worry about getting it (thickness) exactly right the first go. I have a question for you. Are you able to get to the back side of the area you're working? If so you can put a single layer patch on the back side and let it set up before trying to fill the hole. With the size hole your working be sure to grind back a good bit for your patch to really get a good grip, I would grind it back 4 or 5 inches on a 1/4 -3/8" hull thickness, more if the hull is 7/16" or more. I use nonblushing Epoxy so it's not a problem once it starts to cure I can add layers to build up the thickness. Don't try to get the patch level or smooth with the hull, build it up so that you can sand it down to fair it, this may save you a couple of steps. Just a note , I always have trouble making a thick patch hang onto the hull when trying to fill the void at one time. I find it easier to do the repair in two or three steps. But then I'm a novice ,hobby boat restorer.
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Re: Filling Old Transducer Hole

Post by John, CD28 »

Thanks Carl.

Yes, I can get to the inside of the hole - it's under the settee, with good access. I measured the hull thickness to about 7/16". I have it ground back to about a 12" diameter. I hear biaxial should lay up at about 0.040" per layer, so I'm guessing 10 or 11 layers will get me close to 7/16" (0.438"). That's a pretty thick patch, so it'll have some weight. Maybe doing it in a few steps is a good option so it doesn't sag.

Much appreciated!
John
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Re: Filling Old Transducer Hole

Post by Carl-A259 »

You'll do fine John, Do you know if you're using nonblushing Epoxy? If not you'll have an extra step between each lay-up ( not each layer but each series of patches you install after setup or curing has taken place) It will have to be carefully cleaned to remove amine blush, double check with manufactor for the process, it generally is done with soap and water. I don't use that type of Epoxy so I not definite on the process. It's no big deal but it must be done.
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Re: Filling Old Transducer Hole

Post by LazyGuy »

John,

Your hull sounds like my Luders 33. Ten to 12 layers of biax is a bit of overkill, sort of like a 7/16" solid glass hull. So for my 9/16" hull I ground out a bevel to about 10 on the outside and 8" on the inside. Used 3 layers of biax (sufficient for almost any hull) on the outside and let it set. Then I filled what was left of the hole, maybe 1/4 to 3/8" thick with epoxy thickened with cabosil then did 2-3 layers of biax on the inside.

While I understand the desire to repeat the original layup, it would be difficult to convince me that 5 layers of biaxial glass is not sufficient for a 33 foot boat.
Cheers

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Re: Filling Old Transducer Hole

Post by Ed »

John, CD28 wrote: A YouTube video from Jamestown Distributors/West Systems has me confused. The video shows them building/wetting up the new layers of glass on a table, then placing the assembled patch into the beveled hole big circle first. I'm not going to question Jamestown, or West System, but I was thinking the smallest circles of biaxial would go in the hole first with larger circles on top, up to the outer surface of the hull.
Hi John, I watched that video and it's the complete opposite of how I've patched holes for years! And in my old well worn copy of Don Casey This Old Boat, published 1991, on page 71 he shows smallest first. Also around page 58 when installing stiffeners it's smallest to largest. Same with adding lamination for stiffening.
I've done all these things using smallest to largest and also when I butt joint plywood and use fiber glass cloth and epoxy, it's again thinest strip first.
This method makes intuitive sense to me and since I've never experienced lamination failure I'll stick to this process until I see rigorous testing to show the opposite lamination schedule is stronger. Maybe when the basement warms up I'll do a little testing myself:)
Good luck with your project
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Re: Filling Old Transducer Hole

Post by John, CD28 »

Ed wrote: Hi John, I watched that video and it's the complete opposite of how I've patched holes for years! And in my old well worn copy of Don Casey This Old Boat, published 1991, on page 71 he shows smallest first. Also around page 58 when installing stiffeners it's smallest to largest. Same with adding lamination for stiffening...Good luck with your project
You're right Ed - there it is on page 71 of the "Scratch & Itch" chapter! Maybe that's why I was thinking small circle first.

I read somewhere, a few years back, that sweet little Cheoy Lee on the cover of that book was destroyed in a hurricane. Not at sea, but docked or moored along the gulf coast down south.

Somehow I don't think the layup direction had much to do with it. ;)

John
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Re: Filling Old Transducer Hole

Post by CharlieJ »

I don't always agree with Casey. This is one time where I certainly don't. I've ( and all the pros I know) always put the largest patch in first.

And on a thick layup, I'd do it in several stages, mainly to avoid sag and excess heat build up.

And Amine blush comes off just fine with plain old water- nothing need be added. Reference to West System for that.

And as far as I'm concerned there IS no such thing as "non blushing" epoxy. Low blush, perhaps, but I wash as a matter of course- it's way to simple to not do it, and causes too much difficulty if there is blush. Just do it.
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Re: Filling Old Transducer Hole

Post by John, CD28 »

Image

Nothing against Casey - I've learned a lot from his books over the years, still do. But, I'm going in big circle first. I'm going with West epoxy & biaxial, also doing it in two steps as advised by the folks on this board who've done a whole lot more of this stuff than I have.

To start, the inside of the 2" hole will have a bit of plastic (shrinkwrap), a piece of foam, a bit of 1/4" plywood, & a stick pressed in to back it all up.

Where the hull is about 1/2" thick, I'll wet in the outer surface of the hole, then wet in 5 larger patches & put some release cloth over it. Then I'll put some thin 1/2" open cell soft foam, & a thin plastic (1/16" roll up cutting board) over the foam, and tape the plastic sheet to take the shape of the hull. I'm thinking foam and the plastic cutting board sheet will help keep the wet patch pushed up against the hull & minimize sagging. I'll give it a few days to cure, then wash off the amine, scuff up the surface, and wet in the 5 or so smaller patches, backed up again by release sheet, foam, and cutting board again. This should leave about 0.100" space for the two part epoxy fairing compound (Interlux "Watertite Epoxy Filler").

If it all goes horribly wrong I can always grind it out & start again - lots of room for grinding on a 36.

Wish me luck! (<-- I should just add this as a permanent part of my signature line ;)
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Re: Filling Old Transducer Hole

Post by Carl-A259 »

OK John, GOOD LUCK!!!
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Re: Filling Old Transducer Hole

Post by earlylight »

I wish you the best.
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Re: Filling Old Transducer Hole

Post by John, CD28 »

Image

Image

Yeah, I think that worked. I wet in the 5 big circles first & let it cure overnight with release cloth on top. The release cloth peels off & leaves a nice fine weave texture surface. Then I washed the amine off, let it dry, and wet in 6 smaller circles capped off with release cloth again (still in picture), 11 layers of biaxial in all.

I just need to remove that release cloth, wash the amine off, & fair it out even with the gel coat. I'll use epoxy fairing compound and a good fairing batten for that. A little sanding & she'll be done.

Thanks All!

John
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Re: Filling Old Transducer Hole

Post by Carl-A259 »

Nice work John, I all for going back with cloth for the layup and not just gooping some filler in to level out the patch. Smooth and paint and permanent patch complete.
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Re: Filling Old Transducer Hole

Post by earlylight »

Looking good!
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